U.S. Pat. No. 3,135,716 teaches the preparation of terminally reactive polymers through the reaction of living (i.e. non-terminated) polymers with reagents such as oxygen, sulfur, halogen, sulfuryl chloride, carbon disulfide, carbon dioxide, and carbonyl chloride.
U.S. Pat. No. 3,598,887 teaches a process for making multiblock copolymers by coupling living block copolymers with carbon dioxide, carbonyl sulfide, or carbon disulfide.
U.S. Pat. No. 3,281,383 teaches a method of making a branched polymer by reacting a monolithium non-terminated polymer with a compound having at least three reactive sites capable of reacting with the carbon-lithium bond to produce a "radial" polymer, i.e. a polymer having long chain branches. The types of treating compounds, used included polyepoxides, polyisocyanates, polyimines, polyaldehydes, polyketones, polyanhydrides, polyesters, and polyhalides.
U.S. Pat. No. 3,349,071 teaches a process for reducing the cold flow of diene polymers by terminating lithium catalyzed diene polymers with carbon disulfide.
U.S. Pat. No. 3,427,364 teaches a process for preparing polymers of increased molecular weight by reacting lithium catalyzed non-terminated homopolymers and copolymers of conjugated dienes and mono-vinyl arenes with carbon monoxide as a coupling agent.
In the Journal of Polymer Science, A-1, 6 859 (1968) there is reported the use of diethylcarbonate in an attempt to couple "living" lithium polystyrene for the formation of a ketone-containing polymers, i.e., ##STR1## which could be further used for a grafting reaction. With "living" lithium polystyrene of viscosity average molecular weight, Mv, of 31,500, and an equivalent amount of diethyl carbonate, there was obtained a very modest increase in Mv to 42,800. However, the fractionated polymer from the diethyl carbonate reaction yielded very little graft polymer and therefore, it was concluded in this article that diethyl carbonate was ineffective as a coupling agent. The product resulting from the reaction of "living" lithium .alpha.-methylstyrene polymer of Mv=31,500 and diethyl carbonate has Mv=29,200, representing no coupling. No mention is made of conjugated diene polymers in this article, nor are any additional data or discussion given which would even suggest that diethyl carbonate could function successfully as a coupling agent for broadening the molecular weight distribution of "living" lithium polydienes.
The present invention relates to new compositions and to a process for making conjugated diene polymers having one or more of the following features: broadened molecular weight distribution, enhanced Mooney viscosity, negligible cold flow, and better processability. In another aspect, it relates to a process for preparing branched copolymers having broadened molecular weight distribution and negligible cold flow. During packaging, shipping and storage of elastomeric hydrocarbon polymers, the tendency of these materials to undergo cold flow in the unvulcanized state can present severe handling difficulties. If a package of polymer is punctured, the resulting polymer can flow out, leading to product loss, contamination, or sticking of packages together. Furthermore, hydrocarbon polymers of conjugated dienes of relatively high Mooney viscosities are frequently difficult to process. Their low Mooney viscosity counterparts on the other hand have a tendency to cold flow in the uncured state. This restricts the use of hydrocarbon polymers of conjugated dienes in the manufacture of high impact plastics, such as polystyrene. Linear polybutadienes frequently do not possess the necessary combination of rheological and viscosity properties such as Mooney viscosity, styrene solution viscosity, and cold flow needed in the manufacture of reinforced polystyrene.
We have discovered that the treatment of organolithium catalyzed non-terminated conjugated diene polymers with linear organic carbonates, linear thiocarbonates and linear sulfites produces new polymers possessing broadened molecular weight, enhanced Mooney viscosities, negligible cold flow and greater styrene solution viscosities compared to the untreated polymers. The polymers resulting from our invention possess the desirable processing properties so necessary for conjugated diene polymers used in the manufacture of reinforced polystyrene and for making rubber goods such as tires, conveyor belts and hoses.
Although the use of only organolithium initiators for synthesizing non-terminated polymers has been shown in the experimental portion, the scope of the invention covers the use of other organoalkali metal and organomagnesium initiators.
The microstructures of the polymers prepared from conjugated dienes may be modified by employing polar compounds, known in the art, during polymerization. Some examples of polar compounds are: diglyme (dimethyl ether of diethylene glycol), tetrahydrofuran, triethylamine, and N,N,N',N'-tetramethylethylenediamine.